1. Field of the Invention
The present invention relates to a liquid discharge head configured to discharge a liquid, such as ink, from a discharge port.
2. Description of the Related Art
In recent years, a liquid discharge head has widely spread as an ink jet recording head for discharging ink as a liquid. Further, the liquid discharge head has been in commercial use in the medical equipment field and others for discharging chemicals as a liquid. Attempts for commercializing and popularizing the liquid discharge head have led to a problem of how to make the liquid discharge head at a low cost. In that case, it is effective to miniaturize a discharge element substrate on which discharge elements are disposed. The discharge element generates energy for discharging a liquid. For example, if the discharge element substrate is miniaturized, the number of discharge element substrates that can be formed from a wafer is increased. Accordingly, such miniaturization enables the cost reduction of a liquid discharge head.
However, the miniaturization of a discharge element substrate results in a problem of how to radiate heat from the substrate and to secure a space for disposing an electric connection terminal.
Japanese Patent Application Laid-Open No. 2006-91012 discusses a liquid discharge head capable of solving such a problem. This liquid discharge head includes an electric connection terminal for connecting electricity to the outside and a structure for radiating heat on the back side of a discharge element substrate. The back side of the discharge element substrate does not include an electric circuit and a flow path structure for discharging a liquid. Furthermore, Japanese Patent Application Laid-Open No. 2006-91012 discusses a liquid discharge head 600 as illustrated in FIG. 15. The liquid discharge head 600 includes four discharge element substrates 601 mounted on a supporting member. Each discharge element substrate 601 is provided with one liquid supply port 602. The supporting member 603 is made of a ceramic sheet laminated body in which a through-hole 604 for supplying a liquid and an electric wiring 605 are incorporated.
However, progress in miniaturization of a liquid discharge head results in a configuration in which one discharge element head substrate is provided with a plurality of liquid supply ports. This configuration also narrows the interval between through-holes of the ceramic sheet laminated body, which communicate with the liquid supply ports. An ink jet recording head, which is an example of a liquid discharge head, also tends to lengthen a discharge element substrate (recording element substrate) for attaining high-speed recording and to form a number of ink discharge port arrays on the recording element substrate for attaining a high-quality image. For this reason, a ceramic sheet laminated body will include a plurality of long and thin through-holes (ink flow paths) at a narrow pitch.
As a result of driving for liquid discharge, heat generated by an electric circuit and an element which generates discharge energy is transferred from a discharge element substrate to a ceramic sheet laminated body. However, a narrow partition wall between through-holes of the ceramic sheet laminated body, which provides a heat radiation path, results in a problem that it is difficult to radiate heat sufficiently.
Concerning this problem, in a more miniaturized ink jet recording head, a long and thin partition wall is formed along ink discharge port arrays (that is, along an ink supply port). Accordingly, after heat is transferred to the partition wall, a through-hole (ink flow path) blocks the heat transfer. As a result, heat is almost transferred along the longitudinal direction of the partition wall. In such circumstances, the discharge of ink will cause a rise in temperature at the center part in a longitudinal direction of the partition wall, because the radiation of heat at the center part in a longitudinal direction of the recording element substrate is not sufficient.
Such a high temperature rise may generate failures, such as occurrence of a faulty operation of a circuit formed on the recording element substrate, degradation of image quality due to variations in temperature in the longitudinal direction, and difficulty in discharging ink due to air bubbles remaining in a ink flow path.
This provides an important problem in a liquid discharge head which discharges ink using thermal energy generated by a heating element. This is because unless a region located around the heating element sufficiently performs heat radiation, the temperature of the region rises instantaneously.